Document inline file/index behavior.

README.org

@@ -138,6 +138,10 @@ entry under key is found (like in ~gethash~).
   (njson:jget #p"/second-key/0" data)
   ;; => 1, T
 
+  ;; Can decode and index files as an alias for `njson:decode'.
+  (njson:jget #(0 "kind") #p"tests/baker.json")
+  ;; "Listing"
+
   ;; Modify the element in place:
   (setf (njson:jget #p"/second-key/0" data) 3)
   ;; Another indexing syntax, for no particular reason:

functions.lisp

@@ -141,6 +141,13 @@ KEY-OR-INDEX can be
 - a sequence of integers and strings (to index the nested structures).
 - an empty sequence/pathname (to match the whole object).
 
+OBJECT can be
+- A hash table, indexed by strings
+- An array, indexed by integers
+- A stream, which is `decode'd and then indexed
+- A pathname, which is `decode'd and then indexed
+- Anything else, considered an error (see below)
+
 Return two values: the value under KEY-OR-INDEX and whether this value
 was found.